A camera module is equipped in various electronic devices such as TVs, mobile terminals, vehicles, home appliances, and the like. A wavelength of light used by the camera module may differ according to a characteristic of each electronic device. For example, a camera module for acquiring an image using visible rays uses an infrared (IR) cut filter, and an IR camera for acquiring an image using infrared rays uses an IR band pass filter for cutting light with different wavelengths except for the infrared rays.
The related art camera lens uses a method of merging color images by blocking non-imaging optical noise using an IR cut filter that is a flat device disposed between an imaging lens and an image sensor for cutting IR rays.
The device for cutting the IR rays is typically disposed between the imaging lens and the image sensor, but alternatively configured in a manner of being coated on a surface of a lens without using the IR cut filter, in a manner of arranging the IR cut filter on an IRIS of a lens center portion. Also, the device for cutting the IR rays is also configured in a form of a cover glass on an outer side of a camera so as to block (cut) the IR rays. For CCTV, an IR filter employing a day & night switching method, so-called a day & night meter, is used between the imaging lens and the image sensor.
The IR cut filter cuts IR rays in a reflection-coating manner. However, the scattered reflection of the cut IR rays is introduced into the image sensor and often serves as noise light. Accordingly, for a high-resolution camera and a high-end camera which attaches great attention to performance, an absorption filter that absorbs IR rays by a material characteristic is sometimes used, instead of the reflection-type IR cut filter.
In proportion to an incidence angle of light that is incident on a lens, an exit angle (CRA) of light passed through the lens increases. According to this principle, if a size of the lens itself is reduced, the exit angle (CRA) of light which passes the closest area to an edge of the lens increases.
Meanwhile, a transmission characteristic of a filter differs according to an incidence angle (substantially the same as CRA) of light reaching a filter. Therefore, a wavelength shift is caused at a peripheral (or surrounding) area of the filter at which light arrives at a great incidence angle, which results in failing to cut IR rays to be blocked or cutting IR rays to be transmitted. This causes optical noise.